United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA-822-R-02-023

March 2002

Methods for evaluating wetland condition

#13 Biological Assessment

Methods for Birds
United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA-822-R-02-023

March 2002

Methods for evaluating wetland condition

#13 Biological Assessment

Methods for Birds

Principal Contributor

Department of Fisheries and Wildlife, Oregon State University

Paul R. Adamus

Prepared jointly by:

The U.S. Environmental Protection Agency

Health and Ecological Criteria Division (Office of Science and Technology)

and

Wetlands Division (Office of Wetlands, Oceans, and Watersheds)
United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA-822-R-02-023

March 2002

Notice

The material in this document has been subjected to U.S. Environmental Protection Agency (EPA)

technical review and has been approved for publication as an EPA document. The information

contained herein is offered to the reader as a review of the “state of the science” concerning wetland

bioassessment and nutrient enrichment and is not intended to be prescriptive guidance or firm advice.

Mention of trade names, products or services does not convey, and should not be interpreted as

conveying official EPA approval, endorsement, or recommendation.

Appropriate Citation

U.S. EPA. 2002. Methods for Evaluating Wetland Condition: Biological Assessment Methods

for Birds. Office of Water, U.S. Environmental Protection Agency, Washington, DC. EPA-822-R02-023.

This entire document can be downloaded from the following U.S. EPA websites:

http://www.epa.gov/ost/standards

http://www.epa.gov/owow/wetlands/bawwg

ii
iii

Contents

Foreword ................................................................................................................... iv

List of “Methods for Evaluating Wetland

Condition” Modules................................................................................................. v

Summary ...................................................................................................................... 1

Purpose....................................................................................................................... 1

Introduction: Why Survey Birds? ........................................................................ 1

What Can A Bird IBI (Index of Biological Integrity) Tell You? ................... 1

What Does a Bird IBI Estimate? ............................................................................ 2

Steps in Developing an IBI for Birds .................................................................. 3

Applying a Calibrated Bird IBI .............................................................................. 7

What to Measure ..................................................................................................... 7

Field Survey Protocols ........................................................................................ 7

Research Needs ..................................................................................................... 11

References ..............................................................................................................12

Other Relevant literature .................................................................................15

List of Figures

Figure 1: A Strategy for Locating Bird Point Counts and Area

Counts in a Diverse Wetland....................................................... 10

List of Tables

Table 1: Candidate Bird Metric ...................................................................... 5
iv

Foreword

In 1999, the U.S. Environmental Protection Agency (EPA) began work on this series of reports entitled

Methods for Evaluating Wetland Condition. The purpose of these reports is to help States and

Tribes develop methods to evaluate (1) the overall ecological condition of wetlands using biological

assessments and (2) nutrient enrichment of wetlands, which is one of the primary stressors damaging

wetlands in many parts of the country. This information is intended to serve as a starting point for States

and Tribes to eventually establish biological and nutrient water quality criteria specifically refined for

wetland waterbodies.

This purpose was to be accomplished by providing a series of “state of the science” modules concerning

wetland bioassessment as well as the nutrient enrichment of wetlands. The individual module format

was used instead of one large publication to facilitate the addition of other reports as wetland science

progresses and wetlands are further incorporated into water quality programs. Also, this modular

approach allows EPA to revise reports without having to reprint them all. A list of the inaugural set of

20 modules can be found at the end of this section.

This series of reports is the product of a collaborative effort between EPA’s Health and Ecological

Criteria Division of the Office of Science and Technology (OST) and the Wetlands Division of the

Office of Wetlands, Oceans and Watersheds (OWOW). The reports were initiated with the support

and oversight of Thomas J. Danielson (OWOW), Amanda K. Parker and Susan K. Jackson (OST),

and seen to completion by Douglas G. Hoskins (OWOW) and Ifeyinwa F. Davis (OST). EPA relied

heavily on the input, recommendations, and energy of three panels of experts, which unfortunately have

too many members to list individually:

n Biological Assessment of Wetlands Workgroup

n New England Biological Assessment of Wetlands Workgroup

n Wetlands Nutrient Criteria Workgroup

More information about biological and nutrient criteria is available at the following EPA website:

http://www.epa.gov/ost/standards

More information about wetland biological assessments is available at the following EPA website:

http://www.epa.gov/owow/wetlands/bawwg
v

List of “Methods for Evaluating Wetland

Condition” Modules

1 ................. Introduction to Wetland Biological Assessment

2 ................. Introduction to Wetland Nutrient Assessment

3 ................. The State of Wetland Science

4 ................. Study Design for Monitoring Wetlands

5 ................. Administrative Framework for the Implementation of a

Wetland Bioassessment Program

6 ................. Developing Metrics and Indexes of Biological Integrity

7 ................. Wetlands Classification

8 ................. Volunteers and Wetland Biomonitoring

9 ................. Developing an Invertebrate Index of Biological

Integrity for Wetlands

10............... Using Vegetation to Assess Environmental Conditions

in Wetlands

11 ............... Using Algae to Assess Environmental Conditions in

Wetlands

12 ............... Using amphibians in Bioassessments of Wetlands

13 ............... Biological Assessment Methods for Birds

14 ............... Wetland Bioassessment Case Studies

15 ............... Bioassessment Methods for Fish

16 ............... Vegetation-Based Indicators of Wetland Nutrient

Enrichment

17 ............... Land-Use Characterization for Nutrient and Sediment

Risk Assessment

18 ............... Biogeochemical Indicators

19 ............... Nutrient Load Estimation

20 .............. Sustainable Nutrient Loading

Module # Module Title
1

Summary

Birds potentially detect aspects of wetland

landscape condition that are not detected by the

other groups commonly used as indicators.

Moreover, birds are of high interest to a broad

sector of the public. When using birds as indicators, one must pay particular attention to issues of spatial scale. This requires an understanding of home range sizes of the bird species

being surveyed. The development of wetland

and riparian bird indices of biological integrity is

still in its infancy, but holds considerable

promise.

Purpose

This module is intended to suggest study designs and data collection procedures that might

be used when constructing and testing a regional

index of biological integrity, using birds as indicators.

Introduction:

Why Survey Birds?

n The public notices birds and often becomes

concerned when they die or disappear.

n Birds can indicate the integrity (health or condition) of a landscape in addition to the integrity of individual wetlands. Assessing integrity of landscapes (watersheds or other areas

many square miles in size) is vital to assessing

the cumulative effects of human activities.

n Most birds are easy to survey: there is no need

to collect and analyze samples or struggle with

complex taxonomic keys.

n A relatively large pool exists of interested data

collectors, many of whom are proficient at bird

identification or can be trained. They often

are eager to help with surveys, sometimes on

a volunteer basis.

What Can a Bird IBI

(Index of Biological

Integrity) Tell You?

I

n contrast to chemical monitoring, a bird IBI

can tell you, simply and directly, the condition

of living systems at a site (an individual wetland)

or in a landscape of interest. Such knowledge

is more direct and more integrative than information merely about a site’s contamination status. A well-conceived, adequately validated bird

IBI considers a whole host of natural and human environmental influences to indicate if a

landscape is currently supporting an integrated

and adaptive biological system. Such an index

is of practical use in several contexts:

n Protection Priorities, Cleanup Priorities, and

Section 305(b) Reporting: Are wetlands in

watershed “X” generally more degraded by

human alteration than those in watershed “Y”?

n Restoration Progress: Have efforts to restore

wetlands A, B, and D succeeded in establishing representative bird communities?

n Trends: Over a multiyear period, are we maintaining or improving the biological quality—

not just the quantity—of our region’s wetlands?

Though not a panacea, IBIs do embody the concept that biological condition, as represented by

bird species composition and species characteristics, can reflect the relative degree of human

alteration. When used together with other assessment tools, IBIs simplify and summarize complex

biological information so it can be understood and

used more readily by resource managers.
2

The development of wetland and riparian bird

IBIs is, unfortunately, still in its infancy. Thus

information in this module is based mainly on a

healthy dose of ecological theory, monitoring experience, and just a few studies (notably

O’Connell et al. 1998, Rottenborn 1999, Richter and Azous 2001). In contrast to the few IBIoriented studies of birds, agencies have eagerly

supported the development and testing of regional IBIs for fish and stream invertebrates for

over 15 years.

What Does a Bird IBI

Estimate?

C

ollectively, birds are sensitive both directly

and indirectly to a variety of environmental

influences (Adamus and Brandt 1990):

n Vegetation extent, pattern, and structure, especially woody and robust herbaceous vegetation (Finch 1991)

n Water extent, depth, duration, and seasonal

frequency (Wakeley and Roberts 1994)

n Salinity (Halse et al. 1993)

n Water quality, i.e., nutrient loads, anoxia, water clarity, acidity, contaminants, sedimentation (Hoyer and Canfield 1994, Rushton et al.

1994, Savard et al. 1994)

n Disturbance by traffic, persistent human visitation, and associated predatory animals (Craig

and Barclay 1992, Reijnen et al. 1995, Miller

et al. 1998)

It is not always possible to establish with certainty which of the above (or other) environmental influences is causing a bird IBI to have a low

value. A bird IBI usually cannot prove causeeffect connections. However, once general impairment has been established using an IBI, more

intensive studies may be desired to diagnose specific causes. Moreover, in many situations it is

not necessary to define specific causes of impairment. Birds are valuable as an indicator precisely because they are integrators of the cumulative effects of multiple environmental influences

in a landscape. For example, based on

regionwide surveys, one study (O’Connell et al.

1998) quantified regional landscape integrity in

avian terms as follows:

Among other distinct characteristics, a

significantly greater percentage of the

species observed at these [highest quality] sites are insectivorous, forage in decaying tree bark, and migrate from distant wintering grounds, than those observed at other sites. This partial profile

tells us these habitats support upper levels of the food chain, trees in advancing

stages of age and decay, and songbird

species with continental range. As such,

these habitats exhibit important functional, structural, and compositional elements of biological diversity. At the

other end of the spectrum, 27% of the

survey sites exhibited low ecological integrity. A significantly greater percentage of species observed at these sites are

omnivorous, non-native, reproduce multiple times per season, and parasitize or

prey on the nests of other birds. This is a

classic profile of opportunistic behavior,

and is observed in both plant and animal

species when habitats are disturbed by

human or other events.

Blue-winged Teal
3

Because many bird species are long-lived and

migrate annually between continents, it is likely

that the status of some species in a particular

area may be influenced as much or more by the

conditions in their wintering or summering areas as by the conditions in the study area (Finch

and Stangel 1993). However, this factor’s effect on a bird IBI may be lessened by surveying

a sufficient number of sites throughout a region

during IBI development.

The boundaries of the “landscape” whose condition is being represented by a bird IBI will depend on characteristics of the particular bird species that are present (Hansen and Urban 1992).

For example, bird IBI values for a site inhabited

2

 Identify at least 10 sites of that class that

seem potentially to be the most altered1 by

humans, 10 that seem the least altered, and

10 with a potentially intermediate condition

(these numbers are arbitrary and it is not essential that they be equal or that 30 sites be selected).

Eliminate from further consideration sites that

cannot be accessed because of ownership restrictions or hazards. In some situations it may be

possible to predict fairly precisely the number of

sites that need to be surveyed by using prior estimates of spatial and temporal variability from

mostly by particular small, strongly wetland-dependent birds that wander little during the breeding season (e.g., rails, some sparrows) may reflect more the condition of the particular site than

the condition of surrounding uplands,that is, the

broader landscape. The opposite is true for sites

inhabited mostly by particular large birds that

wander greatly (e.g., raptors, shorebirds, waterfowl). Thus, in most instances, a bird IBI should

be segregated into components that reflect these

two (or more) scales. Alternatively, the IBI

should use data only from species that characterize a particular scale, so that the area (or species group) whose integrity the IBI is representing is clear to users.

Steps in Developing an

IBI for Birds

1

Within an ecoregion (a region of gener

ally similar physiography, land use, and

climate) decide on what basis you will

group (classify) wetlands into types (classes).

Wetlands may be classified based on vegetation,

water regime, or a host of other factors. Choose

the factor(s) that best account for the naturally

occurring, within-class variability in bird species

composition. To accomplish this, consider using the classification of Cowardin et al. (1979,

as used on National Wetland Inventory maps),

Brinson (1993, the hydrogeomorphic or HGM

classification), or others described in the Classification module. Then focus your sampling on

one class, for example, flow-through riverine

wetlands dominated by woody vegetation. The

more narrowly you define your target class, the

more likely you are to find effective bird metrics

(because you have constrained natural variability). However, the utility of the resulting metrics

will be limited because they address only that

one class.

1 The criteria for prejudging which sites are least or

most altered necessarily will be subjective, and it

may be helpful to prepare and apply a standardized,

semiquantitative checklist for systematically evaluating potential impacts at all candidate sites (e.g.,

Bryce et al. 1999). The inventory of alterations

should include indicators of human disturbance

thought most likely to have an impact on birds, for

example, densities of houses and roads, proximity to

houses and roads, percent of land that is

nonvegetated or mowed lawn; and habitat patch

area, perimeter-area ratio, width, and connectivity to

similar patches (Robinson et al. 1995, Miller et al.

1997, Germaine et al. 1998, Helzer and Jelinski

1999). See the Developing Metrics and Indexes of

Biological Integrity module for further information

on characterizing alteration.
4

similar wetland types in the same region. For

some wetland bird metrics, such variance estimates are compiled in Adamus and Brandt 1990

(Tables 15 and 16 of that report) and Adamus

1996 (Appendix N of that report). Visit the selected sites to confirm the accuracy of the ecological classification and apparent alteration.

Alternatively, you may select fewer sites but collect data both during prealteration and

postalteration years (e.g., Richter and Azous

2001). Occasionally, it may be feasible to analyze existing databases to identify assemblages

of species that are most sensitive to particular

types of alterations (e.g., Burdick et al. 1989).

For example, if you are aware that economic,

legal, or policy factors resulted in a surge in

wetland drainage, wetland restoration, landclearing, or construction in a particular county

between 1985 and 1990, you might determine if

Breeding Bird Surveys (BBS) or Christmas Bird

Counts (CBC) were conducted in the county before, during, and after that period (this determination can be made by visiting <http://

www.mbr.nbs.gov/bbs/bbs.html> for the BBS

data or <http://birdsource.tc.cornell.edu/cbcdata/

> for the CBC data). If so, you may be able to

download the data and look for trends in individual species and species groups, being careful

also to examine the possibility that apparent

trends might be the result of interannual changes

in the level of precipitation, the observers involved, the survey date, or other factors (Sauer

and Droege 1990). From such a review, you

may be able to characterize species as “adapters,” “exploiters,” or “avoiders” (Blair 1996) and

then use these designations as bird metrics in a

multimetric index to be tested at other sites.

3

 Conduct equal-effort surveys of birds,

applying the same methods to all chosen

sites (see Field Survey Protocols, below).

4

 During at least one site visit, estimate the

extent and condition of structural attributes,

both within and around the wetland, that

potentially constitute habitat for most expected

species (Morrison et al. 1998). If unsure, consult with local birders and ornithologists. Attributes likely to be particularly important are

the acreages of standing open water (permanent

as opposed to seasonal); woody vegetation (riparian as opposed to upland and various age

classes), cropland, and unmanaged fields; proximity to similar wetlands and other natural habitats; the cumulative length of roads, ditches, and

streams; presence of fish; and the number of residences and vegetation strata (layers) (Craig and

Beal 1992, Lovvorn and Baldwin 1996, Weller

1999). These features should be assessed both

within the site and, if possible, through aerial

imagery in concentric zones at various distances

from the site, up to perhaps 1 mile away. Distribution of surface water should be assessed during both wet and dry seasons whenever possible.

Suggestions for assessing many habitat features

is provided by Bookhout (1994).

5

From the collected data, identify species

and groups of species whose attributes

(e.g., presence, abundance, frequency) are

clearly skewed towards the most—or least—altered sites, or identify the years with most and

least alteration. Do not rely too heavily on statistical correlation; more important is the presence or absence of particular species or groups

exclusively at either the least or most altered sites.

Also important is the proportional distribution

of abundances of species at these sites (i.e., bird

community “evenness”). When only one or a

few species dominate a site numerically, it sometimes indicates broader degradation of the site’s

ecological systems. Such a diagnosis depends

on the particular species and habitat type. See

the Developing Metrics and Indexes of Biological Integrity module for further information on

interpreting data.
5

6

 Try creating “metrics” by pooling data

from groups of species. Define the groups

based on similar life history, home range

size, or other behavioral or demographic characteristics (Croonquist and Brooks 1991,

Mulyani and DuBowy 1993, Bournaud 1994,

Weller 1995, Wiens et al. 1996). Metrics are

attributes shown empirically to change in value

along a gradient of human disturbance. Examples

might include those shown in Table 1 (these are

not comprehensive and most have not been validated). Analysis of data from mainly upland landscapes suggests that resident species may be less

affected than migrants by habitat structure as

measured at a landscape scale (Flather and Sauer

1996).

Be sure that candidate metrics do not, as a whole,

imply that sites are in better ecological condition

only because they are wetter, or have closed

canopies. Some wetland bird species are

naturally adapted to dryer sites or sites with no

trees or no vegetation at all, as in the case of

many shorebirds (Rottenborn 1996). Prolonged

duration of inundation, or invasion by trees or

even low emergents, actually may signal

degradation of their associated wetland class.

Thus metrics that express only species richness

without accounting for the characteristics of the

component species, and thus which may reflect

only the area of habitat at a site and its natural

structural complexity rather than ecological degradation (Findlay and Houlihan 1997, Warkentin

and Reed 2000), may yield information that is

less useful (Meiklejohn and Hughes 1999,

Attribute Hypothesized Relationship

to Environmental

Degradation

Frequency of occurrence of species that are insectivorous aerial foragers decrease

Percent of species that are long-distance (e.g., Neotropical) migrants decrease

Proportional abundance (%) of blackbirds and starlings increase

Ratio of juvenile to adult-plumaged diurnal raptors decrease

Cumulative frequency of occurrence of all regionally rare species decrease

Number of species that typically feed on submersed aquatic vegetation decrease

Proportional abundance (%) of the three most common species increase

Frequency of occurrence of reputedly egg-predating or parasitizing species

(e.g., corvids, cowbirds, marsh wren) (Rogers et al. 1997)

increase

Number of found species that have shown statistically significant declines in the region

according to BBS data

decrease

Percent of found species that also are regularly present on >90% of the BBS routes in

the same region (“core” species, Collins and Glenn 1997)

increase

Percent of the expected species (based on geographic range, wetland type, vegetated

area, and other variables) that were found (e.g., “Avian Richness Evaluation Method”

of Adamus 1995, “Index of Avian Integrity” of Schroeder 1996)

decrease

Genetic diversity among found species, as assumed from their phylogenetic

relationships (“functional integrity,” von Euler 1999) decrease

Table 1: Candidate Bird Metric
6

Whitaker and Montevecchi 1999). Moreover, a

variety of wetland types, regardless of their

internal heterogeneity, is essential to supporting

biodiversity at regional scales (Leonard 1994,

Haig et al. 1998, Warnock et al. 1998).

7

 Using data plots and statistical analysis,

verify that the alteration category, rather

than a wetland habitat feature such as acreage or seasonal duration of standing water, was

associated strongly with the apparent affinity of

some birds for most or least altered sites or years.

If the alteration category is associated with species affinity, proceed to step 9. If not, go to step

8. This verification step is unnecessary if previously it was demonstrated that the correlated

habitat feature’s condition is governed entirely

by human alteration. Ideally, it is best to examine the relationship of bird metrics to alteration

category and habitat structure over a multiyear

period (Gibbs et al. 1991, Wilson et al. 1998).

Many good sources are available for planning

and conducting a statistical analysis of data, for

example, Verner et al. (1986), Ramsey and

Schafer (1997), and Nur et al. (1999).

8

 If your extensive review of data plots and

statistical analysis results shows that no

species or grouping of species has a consistent tendency to occur at the most or least

altered sites, it may be because prolonged alteration has eliminated all sensitive species from

the local landscape (Freemark and Merriam

1986). Or, it may be that human factors have

not yet begun to affect local bird communities.

Either possibility is impossible to prove. You will

need to survey additional least-altered sites (if

the first situation seems more likely) or additional

most-altered sites (in the second situation). To

identify these sites, you may need to expand the

study region or broaden the wetland class you

are examining and then repeat steps 6 through

8. You also will need to survey additional sites

if the spatial distribution of all species and groupings seems related more to particular habitat features than to an alteration regime unrelated to

these features. An appropriate classification of

sites prior to sampling can avoid this situation.

Alternatively, you may consider dividing the

wetland class into habitat subclasses and calibrating separate IBIs for each (e.g., for shallow

and deep wetlands). This, too, would require

surveys at additional sites, so it is best to anticipate and address such factors during the study

design phase, before beginning the surveys.

9

Propose a simple mathematical formula

 and try several ways of combining the

metricsinto one or more “multimetric indices,” after first standardizing each metric with

respect to its numeric range. A multimetric index might consist, for example, of the sum of

individual metrics such as (a) the number of species that are long-distance migrants and (b) the

percent of total abundance consisting of aerial

foraging species, divided by (c) the frequency of

the European Starling. It is not necessary for

the individual metrics to be logically or mechanistically interrelated as in classical ecological

models, but alone they should have a relationship to human disturbance of wetlands that is

supported at least by ecological theory and ideally by experimental data. Separate multimetric

indices may be warranted for different measurement scales (site versus landscape) and different seasons, depending on the particular regional

avifauna. Iterative experimentation and adaptation are important in identifying the most sensitive and consistently accurate indices. The best

multimetric index will be one that responds most

sensitively to the human disturbance gradient,

independent of habitat conditions that are unrelated to alteration. A multimetric index that

comprises at least six bird metrics, each measuring a unique type of avian response to human

alteration, is most likely to show adequate sensitivity in future applications.
7

Applying a Calibrated

Bird IBI

O

nce a bird IBI has been developed, or an ex

isting bird IBI has been calibrated for local

conditions, you will apply it during routine site

assessments by conducting bird surveys at a probability sample of sites (e.g., a statistically random selection of accessible sites) whose degree

of alteration is unknown. The surveys should be

conducted using the same methods used when

developing the bird IBI, and it may be possible

at this point to conserve effort by focusing on a

narrower range of species or species groups—

those found during IBI development to be most

reliable as indicators. Then organize the collected

data according to the metrics in the bird IBI, and

compare the site’s values for these metrics with

the range of regional values embodied in the bird

IBI previously developed from multisite or

multiyear data.

What to Measure

n Abundance of each species and number of species—appropriate for reconnaissance-level

surveys (one-time visit)

n Frequency of occurrence, by species and season—if additional resources are available for

more frequent surveys

n Duration of wetland use by individual birds—

feasible only if professional biologists can distinctively band or otherwise mark individual

birds, but potentially the most diagnostic attribute

n Behavior of individual birds (e.g., feeding,

resting)—feasible only where nearly all individuals can be viewed

Many other features of bird populations can be

indicative of wetland degradation, but they are

not described here because their requirements

for specialized equipment, skills, or time makes

them unsuitable for use in routine regional-scale

monitoring programs.

Field Survey

Protocols

T he following are recommendations basedpartly on accepted bird survey protocols

from nonwetland habitats, for example, Ralph et

al. (1993, 1995), Bibby et al. (1992), as well as

some techniques applied specifically to wetlands

(Ribic et al. 1999, Weller 1999). They have been

tempered to reflect what we have learned so far

from surveying wetland birds. These protocols

will not apply equally well in all situations and

will likely evolve as we learn more.

Birds in wetlands are best inventoried using area

searches or point counts.

Area searches (also called “direct counts,”

Weller 1999) are appropriate for the parts of

wetlands where visibility is unobstructed, such

as open water areas, mudflats, and short-grass

flats (e.g., Igl and Johnson 1997). Species

are counted based on visual, not auditory, identification.

Point counts can include all habitats within a

site and are especially appropriate where visibility is partly obstructed by trees, shrubs, and/

or tall grasses. Species that are seen or heard

are counted.

Area searches involve using a spotting scope

or binoculars to scan the open area from one or

more fixed points, generally viewpoints with the

best visibility of the site and whose fields of vision do not overlap. Occasionally, area searches

will involve canvassing an area by boat, aircraft,

or by walking. Birds should be identified and
8

counted until all individuals within the field of

view have been tallied. The time required to

complete the count should be recorded and the

exact size (hectares) of the scanned area should

be measured (e.g., from aerial photographs or

field sketches). These estimates of area searched

and time spent should be used as covariates in

the statistical analysis, or less desirably, used to

derive variables such as “birds per minutes

searching” and “birds per hectares scanned.” To

facilitate later data interpretation, the search area

(and associated data collection) may be subdivided into individual habitat types. Area searches

may be used in wetlands of any size wherever

views are unobstructed. They are not effective

for surveying most songbirds, which constitute

the majority of species in many wetlands.

Point counts also involve tallying birds from

fixed points, but require the observer to identify

all species by sound as well as sight. Standard

protocols for terrestrial point counts specify that

birds be tallied for 5 minutes at each point (some

biologists prefer 10 minutes). Usually, no two

points should be closer than 200 m to each other

(Ralph et al. 1995). Thus the number of points

allocated to any wetland will depend on wetland

size. This requirement also implies that, if the

objective is to sample only the wetlands and not

the adjoining uplands, ideally, the wetlands must

be no less than 8 acres in size (if perfectly round;

much larger if not) in order to situate points more

than 100 m from the wetland-upland edge.

Some researchers also recommend that observers estimate distance to each identified bird regardless of wetland size (Emlen 1971), or at least

differentiate between individuals detected within

25, 50, or 100 m and those farther away (Hodges

and Krementz 1996). This step may be particularly important if an IBI is to include abundance

(density) metrics or if the species that are being

surveyed differ greatly with regard to their ability to be detected.

Points may be located along a transect (e.g.,

Dickson 1978, Niemi and Hanowski 1984). With

transects, birds detected while the observer was

walking or canoeing between points usually are

recorded as well. There is no technical or statistical advantage to using transects rather than

point counts and area counts alone, and there

are significant disadvantages. Using transects

reduces the flexibility needed to situate points in

the full range of hydrologic zones and vegetation strata within a wetland. Although some

transect protocols allow for including individual

birds observed between points, such observations

must be analyzed separately from observations

made at the points, because of the possibility of

double-counting of individuals located closer

together than the required 200 m separation distance.

Data from area searches and point counts

should not be combined. Also, the need to situate point counts no closer than 100 m from the

wetland-upland edge is a significant constraint.

Researchers who use point counts in smaller

wetlands sometimes include upland habitats as

well (Smith 1998). Or they attempt to distinguish

birds heard from within a wetland from those

heard only from the adjoining upland and analyze just the within-wetland data. Surveys of

small wetlands also are likely to result in encounters with few species: the usual tendency is for

avian richness to increase with patch size. Low

richness in wetlands that are very small or that

have very simple vegetation structure can distort some of the candidate metrics, for example,

calculating the percentage of bird species that

are nonnative, when only two species are

present. To mitigate this problem, during the

data analysis phase it may sometimes be appropriate to analyze data only from sites that meet

minimum thresholds for number of species and/

or individuals.
9

Regardless of the methods chosen, all sites

should be visited within a few-day period (no

more than 1 week). Otherwise, changing weather

and migration can make the data almost impossible to interpret correctly. If an IBI will be used

later to monitor interannual changes in wetlands,

it is preferable to use multiple years of field data

to calibrate the IBI initially.

Unless you intend to survey the same microhabitat (e.g., herbaceous plants in permanently

inundated areas) in every wetland, point counts

and area searches should be used in a complementary manner to survey each of the following

zones if they are present, accessible, and survey

points can be separated by at least 200 m: (1)

permanently inundated areas, (2) seasonally inundated areas, (3) areas saturated but seldom

inundated. Secondarily, point counts should be

located collectively so that they are within (or

no more than 100 m from) each of the following

vegetation strata (cover types), if present within

a site:

n Herbaceous plant communities (aquatic or terrestrial) not under a woody canopy, if not already covered by an area search.

n Herbaceous plant communities (aquatic or terrestrial) under a woody canopy

n Shrub/vine stands not under a tree canopy if

not already covered by an area search.

n Shrub/vine stands under a tree canopy

n Open-canopy stands of trees (both deciduous

and coniferous)

n Closed-canopy stands of trees (both deciduous and coniferous)

For purposes of IBI development, within these

three zones and six strata, points usually should

not be located randomly, but rather in a manner

that the investigator anticipates will yield cumulatively the most species. Often, this objective

can be accomplished by strategically placing points

between adjoining vegetation strata (Figure 1).

However, if quantitative metrics (e.g., relative

abundance) will be used later in multimetric indices, then random or systematic location of sampling or observation points within zones may be

justified and a much larger number of samples will

be necessitated.

When comparing sites (separate wetlands), data

from the sites should represent equal effort. For

example, it is inappropriate to make comparisons using seven survey points from a large site

but only two survey points from a smaller site,

or five visits to one site but only two to another

during the same month. In such situations, compare the sites based on a single point or date chosen randomly from those at each site, or include

a log of the area as a covariate in the statistical

analysis. Alternatively, you might select from

each wetland the point or date you found to have

the highest counts of birds, or a point believed

to be of exactly the same habitat type in all the

surveyed sites. Such practices are not recomBlack Rail by Thomas J. Danielson
10

mended for use when statistical confidence is

needed from monitoring a probability sample of

wetlands, but they may be acceptable in some

situations involving IBI development and

testing.

If possible, sites in a multiwetland survey should

be visited all on the same day, or on consecutive

days, unless severe weather conditions intervene.

Concentrated visits are necessary because, especially during migration, the numbers and species composition of bird communities shift on a

daily or even hourly basis. At the very least,

date and time of day (in standardized units)

should be included as covariates in statistical

analyses. Additionally, sites that are accessed all

on the same day should be revisited in a different

sequence on each successive visit.

Ideally, all sites could be visited monthly for an

entire year and separate IBIs calibrated for each

season. However, at a minimum, all sites should

Figure 1: A strategy for locating bird point counts and area

counts in a diverse wetland.

Point counts (P1, P2, P3) must be located no closer than 200 m from each other, and preferably at least 100 m from the wetlandupland edge, so point counts cannot be used effectively unless the wetland is at least 8 acres (if round, much more if narrow). They

should lie within (preferably) or within 100 m of each of the major hydrologic zones (H = permanently inundated; B = seasonally/

semipermanently inundated; C = saturated only) and each of the major vegetation strata (FO = forest; SS = shrub/scrub; Em =

emergent). Point counts are primarily intended to survey passerine species.

Area counts (A1, A2) should be located at the best vantage points for surveying birds on all bodies of open water (W-H) as well as

in permanently inundated stands of emergent vegetation within the site. Area counts are intended to survey only the most visible

waterbirds (e.g., ducks, herons, shorebirds). Area counts need not be a specific distance apart, so long as observers avoid overlapping the visual count areas. Area counts may be located next to point counts or in adjoining uplands. Abiding by these constraints

and considering physical access, observers should attempt to survey as many point counts and area counts as can be fit into a

wetland site.
11

be surveyed at least twice per season, with at

least 2 weeks elapsed between visits. If data can

be collected during only one season, the breeding season (generally May-July) generally is a

good time, because dispersal movements of most

species are minimal then (Morrison et al. 1998).

By detecting species at the same point during

repeat visits, probable breeding often can be inferred (Vickery et al. 1992). The same observer

should inventory all sites, at least during each

survey period. If multiple observers must be used

(as often is the case when volunteer birders are

assisting), pretesting must verify that their skill

levels, especially with regard to auditory-only

recognition and identification of a wide range of

expected species, are equivalent. If not, new

observers should be recruited, or at the very least,

“observer” should be included as a variable in

any statistical analysis.

Species detection (especially of most songbirds)

is greatest during early morning hours so surveys should focus on the 4 hours beginning at

sunrise. Night-time coverage may be warranted

not only for typically nocturnal species such as

owls but also for waterfowl and wading birds,

which use different wetland types for roosting

and for feeding, especially during the hunting

season (Anderson and Smith 1999). Secretive

species (e.g., rails, some passerines) can be surveyed effectively by broadcasting tape-recorded

calls of the secretive species. A protocol for

doing so is described by Ribic et al. (1999). Also,

during winter and other nonbreeding seasons,

you can induce many species that otherwise do

not vocalize then to reveal themselves by playing tapes of small owl, chickadee, and nuthatch

calls (in alternating sequence). Counts during

the hunting season (generally September-January) should be avoided or, if necessary, some estimation should be made of hunting intensity at

each site.

If three points per wetland are surveyed, approximately 100 easily accessible wetlands in a

local area or small watershed can be visited three

times in a typical field season. Only a fraction of

this number of wetlands need be visited to initially develop and calibrate a regional IBI for a

single wetland class.

Research Needs

The IBIs that have been developed using fish,

algae, and aquatic invertebrates have benefited

from field testing in several regions of the world.

Similarly, the development of operational IBIs

using birds will require commitments to fund

studies in several types of wetland landscapes.

Such studies should examine spatial changes in

bird communities across multiple wetlands that

span gradients of identifiable human disturbance,

as well as interannual changes in altered and unaltered wetland landscapes. The aim of the studies should be to establish which avian groups and

attributes are most regionally suitable as indicators, and at which scales, because of their ability to sensitively distinguish anthropogenic from

Least Bittern by Thomas J. Danielson natural background conditions.
12

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